Light

• Light travels in straight lines from a source
• Light travels as transverse waves
• Light travels much faster than sound
• Light does not need a substance to travel through
• Transparent objects


  Allow light to pass through
• Opaque objects


  Block all light
• Translucent objects


  Allow some light to pass through, but scatter it
• Shadows are made when light is blocked by an object
• Light interactions with materials

  • Transmission
  • Absorption
  • Reflection
• Transmission


  Transparent materials let light pass straight through
• Absorption


  Opaque surfaces can absorb or reflect light
• White surfaces reflect most of the light that hits them
• Black surfaces absorb light very well and reflect very little
• Diffuse reflection


  Light rays are scattered by rough surfaces
• Specular reflection


  Mirrors and shiny materials reflect light evenly
• The angle of incidence is equal to the angle of reflection
• Law of reflection


  The angle of incidence (i) is equal to the angle of reflection (r)
• Angles are measured between the light rays and the normal
• You can see an image in a mirror because the reflected rays of light appear to come from a point behind the mirror
• The image in a plane mirror is the same size as the object
• The image in a plane mirror is the same distance away from the mirror
• In the image, left becomes right and right becomes left
• Refraction


  When light hits something transparent, it changes speed and direction
• Refraction takes place at the interface between two substances
• When light is transmitted through glass, it slows down and changes direction towards the normal
• When light travels back out of glass, it speeds up again and changes direction away from the normal
• Lenses


  Curved pieces of glass or transparent plastic designed to refract light in particular ways
• Converging lenses


  • Make rays of light come together
• Focal point


  The point where parallel rays of light are brought together by the lens
• Focal length


  The distance of the focal point from the centre of the lens
• Uses of lenses


  • Cameras
  • Microscopes
  • Telescopes
• Camera operation


  1. Lens focuses light

  2. Aperture allows light into the camera

  3. Sensor converts light to electrical signals

  4. Shutter opens when picture is taken
• Rod cells


  Detect faint light but not colours
• Cone cells


  Detect the primary colours of red, blue and green
• We see combinations of primary colours as secondary colours (magenta, cyan and yellow)
• White light is a mixture of colours
• Dispersion


  White light can be split up using a prism to give a spectrum of seven colours
• Spectrum of colours


  • Red
  • Orange
  • Yellow
  • Green
  • Blue
  • Indigo
  • Violet
• Objects do not reflect all the colours in light
• White objects reflect all the colours